1. Technical Field
The present invention relates to an optical inner surface measuring device configured to cause a probe to enter into the inner peripheral surface or deep hole of a target object, radiate a light ray to the inner surface or deep hole bottom surface, capture and observe reflection light in a three-dimensional manner, and measure the dimension and geometric accuracy of the target object.
2. Description of the Related Art
For example, the finished dimension and geometric accuracy of a cylinder for an automobile engine significantly influence on power performance and fuel consumption efficiency of an automobile. These finished dimension and geometric accuracy are usually measured with the use of a contact measuring device such as a roundness measuring machine, a surface roughness meter, and a length measuring machine with a linear scale. In recent years, however, there has been provided an optical non-contact measuring device for the purpose of preventing a target object from being scratched.
As a means for observing the presence or absence of scratches on the inner surface of a target object in a non-contact manner, the image diagnostic technique (optical imaging technique) is widely used in manufacture of device machines and in medical practices. For example, as a method for investigating the depth of a deep hole and performing image diagnosis at sites of manufacturing precision equipment, in addition to camera observation with a general endoscope, a light ray is irradiated to capture reflection light by an optical sensor and automatically check for uneven brightness by a computer.
In the medical field, there have been studied and used techniques for observation of affected parts of a human body, such as X-ray CT, nuclear magnetic resonance, OCT imaging (optical coherence tomography) by an endoscope using coherence of light, all of which allow observation of tomographic images.
In the medical field, near infrared rays used as a light source reflect on the metallic inner peripheral surface of a deep hole in a target object, or pass partially through a resin film layer, if any, on the metallic inner surface of the same. Accordingly, it is possible to conduct at the same time three-dimensional shape observation of the inner peripheral surface, measurement of thickness accuracy of the film resin, and observation of a pin hole on the resin surface.
Typical structures of observation devices to which techniques for irradiating a light ray to the inner peripheral surface of a machine device or a machine component and observing or measuring the inner peripheral surface are described as in Japanese Patent No. 4461216, JP-UM-A-4-55504, and JP-A-5-180627, for example.
An optical endoscope probe described in Japanese Patent No. 4461216 is configured such that a reflection film (14) is provided at one end of a motor shaft (5) illustrated in FIG. 1 to radiate rotationally a light ray in 360 degrees. According to this configuration, however, an electric wire or wiring substrates (22) and (23) in a motor (1) block the rotationally radiated light ray, and thus the 360-degree radiation cannot be completely conducted to cause some portions from which no image data is captured.
An inner shape measuring sensor described in JP-UM-A-4-55504 is configured such that a hollow motor (26) provided at a leading edge side of a flexible tube (29) rotates a reflection mirror (20) to radiate a light ray as illustrated in FIG. 1. In addition, four strain gauges (5) illustrated in FIG. 4 measure the dimension (diameter) of the inner diameter of a target object in an XY direction, correct ambiguity in optical measurement values, and display the corrected dimension of the inner peripheral surface on a screen.
However, the requisite geometric accuracy of the inner shape of a target object is generally as high as about 0.05 μm. In this configuration, when the hollow motor (26) rotates at a high speed, the rotation shaft causes a large amount of runout or non-repeatable runout so as not to satisfy the requisite accuracy for the inner shape measurement sensor. Therefore, distortion or noise appears on the collected cross-section shape data of the inner peripheral surface of the target object, which disables acquisition of true measurement values.
An in-tube shape investigation device described in JP-A-5-180627 is configured such that the inside of a tube is spirally scanned with a light beam to obtain and display the inner diameter and three-dimensional shape data of the tube in a non-contact manner as illustrated in FIG. 10. However, JP-A-5-180627 does not propose a mechanism configured to radiate rotationally a light beam. Therefore, when the rotational motor for beam radiation rotates at a high speed, the rotation shaft causes runout or non-repeatable runout, and noise or distortion appears on the collected cross-section shape data of the inner peripheral surface of the target object, which disables acquisition of true measurement values.